NEW YORK (Reuters) - In the fall of 2010, John Grant was rushed to Bellevue Hospital with a shattered skull after being hit by a car in New York City. Grant's partner, Daniel Weiss, arrived at the hospital minutes later, frantic for an update on Grant's condition.

But when Weiss explained who he was, and said that he and Grant had a civil union in New Jersey that effectively gave them the same status as a married couple, the response from Grant's emergency room doctor was, "What is that?"

"In the midst of all of this chaos, this catastrophe, everything kept coming down to the status of our relationship," said Weiss, who works as an immigration lawyer. Grant's sister had to travel to New York from her home in Delaware to sign papers as Grant's next-of-kin, authorizing a craniotomy.

Grant survived the accident, and Weiss said he now carries a health care proxy document -- stating he is authorized to make medical decisions on Grant's behalf -- at all times.

"Frankly, when we had our civil union, I thought it was going to be enough, and the state of New Jersey said, 'This is what you need to do to have all the rights of a married couple,'" Weiss said. "Never in my worst nightmare would I have thought we would have to live through something like this to be proven wrong."

This week, New Jersey's state legislature will vote on a bill to replace civil unions for same-sex couples with marriage, the latest state to take on the contentious issue this year. The Senate will vote on Monday, and the Assembly has a vote set for later in the week.

The New Jersey Senate vote will occur on the same day that Washington state Gov. Christine Gregoire plans to sign a bill that will make Washington the seventh U.S. state to legalize same-sex marriage.

Legislation failed in the New Jersey Senate in 2010. Proponents are more confident this time around of the bill clearing both chambers, particularly in the aftermath of a Gallup poll last year that found for the first time a majority of Americans believe gay marriage should be legalized, with 53 percent in favor.

Even should the bill pass the legislature, however, Chris Christie -- the state's Republican governor -- has vowed to veto it, saying he believes marriage should be reserved for unions between a man and a woman.

Both sides say it is unlikely the Democrat-controlled state legislature will have the two-thirds majority to over-ride Christie's promised veto, and Christie has said gay marriage should be put before New Jersey voters in a referendum.

Christie supports civil unions, and has said same-sex couples should have the same rights as heterosexual couples.

But proponents of the gay marriage law say that civil unions are inherently inferior to marriage, largely because employers, hospitals and the public generally do not recognize civil unions and marriage as being one and the same.

"If you call something by two different words, the assumption is that you mean something different," said Hayley Gorenberg, an attorney at Lambda Legal, which filed a lawsuit last summer -- which includes Weiss and Grant -- to have gay marriage recognized in the state.

Stephen Hyland, a lawyer who specializes in same-sex couples law, said the differences between the two institutions become most clear during the most traumatic or joyful times in a person's life -- during a hospital visit, or when a same-sex couple seeks to register as a couple for a birth certificate.

New Jersey is one of four states that allow civil unions -- an institution set up to give the same rights as civil marriage, while reserving marriage for heterosexual couples.

Delaware, Hawaii and Illinois also allow civil unions, and another six, plus the District of Columbia, allow marriage: New York, Connecticut, Iowa, Massachusetts, New Hampshire and Vermont. These are expected to be joined on Monday by Washington when Gregoire signs that state's law.

Also, at least two other states, Illinois and Maryland, have same-sex marriage legislation under serious consideration.

Some 30 states have banned gay marriage. Last week, California's ban was overturned by a federal appeals court, and the issue could be taken up by the U.S. Supreme Court.

In 2006, New Jersey's high court ruled same-sex couples must be guaranteed the same rights as heterosexual married couples, but left it up to the legislature to address it. That year, the legislature voted to allow civil unions.

Gay couples argued the state had created a two-tier system that was inherently unequal. In many cases -- such as obtaining health care benefits for a partner -- gay couples said the equal rights they are guaranteed by civil unions were not automatically enforced.

Last May, seven gay couples again took the issue to court, calling for marriage rights for gay couples. Gorenberg, the lawyer representing the couples, said she expected the case to come to trial early next year.

Proponents of civil unions as an alternative to marriage argue that, with time, civil unions will come to be better understood -- eliminating the burden on same-sex couples to explain the institution to their employers and others.

Some groups, including some that vigorously opposed the civil unions law five years ago, now say that same-sex couples are seeking to use civil unions as a "stepping stone" to a redefinition of marriage in the state.

"We say that civil unions are working," said Len Deo, the president of the New Jersey Family Policy Council. "Marriage is between a man and a woman. There is no reason we have to defend it to be gender-blind."

He notes the New Jersey Division of Civil Rights have received only about a dozen complaints about civil unions.

(Reporting By Edith Honan; editing by Dan Burns)

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